How do large complex brains evolve? Ask the toothed whales!

A new Emory University study (Release date: Oct. 22, 2004) maps how brain
size changed in dolphins and their relatives the past 47 million years,
and helps to provide some answers to how cetacean species evolved
increasing encephalization (just as the primate line leading to human
beings also evolved increasing encepahlization). Increasing
encephalization over time is not a phenomenon unique to the human species
and lineage.
Marino and her colleagues spent four years gathering the data and tracking
down fossils at The Smithsonian Institution and other museums. A total of
66 cetaean fossil crania were scanned and measured. This subset was added
to brain and body weight data from 144 modern cetacean specimens for a
total sample of 210 specimens representing 37 families and 62 species.
Their work produced the first description and statistical tests of the
pattern of change in brain size relative to body size in cetaceans over 47
million years. They found that encephalization level increased
significantly in two critical phases in the evolution of odontocetes.
"[Modern] dolphin brains are four to five times larger for their body size
when compared to another animal of similar size. In humans, the measure is
seven times larger -- not a huge difference. Essentially, the brains of
primates and cetaceans arrived at the same cognitive space while evolving
along quite different paths" Marino says. "What the data say to me is that
we, as humans, are not that special. Although we are highly encephalized,
it's not by much or for that long compared with odontocetes."
"A description of the pattern of encephalization in toothed whales has
enormous potential to yield new insights into odontocete evolution,
whether there are shared features with hominoid brain evolution, and more
generally how large brains evolve," Marino says.
Marino's previous research has shown how dolphins have the capacity for
mirror self-recognition, a feat of intelligence previously thought to be
reserved only for Homo sapiens and their closest primate cousins.
http://www.sciencedaily.com/releases/2004/10/041027112550.htm
http://www.emory.edu/central/NEWS/Releases/dolphin1098476972.html
Received on Sat Nov 6 00:16:19 2004